Add missing comma to REQUIRED_FILES list.

* elastic_recheck/elasticRecheck.py: There was a comma missing in the
REQUIRED_FILES list that cased the cinder volume log file and syslog log
file names to be appended together. Add the comma to fix the list.

Change-Id: I6aaf745f996e725c529ccd9f8b7444d8b9a5648f